Numerical Investigation on Delamination Induced by Thermal Mismatch in Epoxy Impregnated REBCO Pancake Coils

In this study, the stress and delamination properties in epoxy impregnated REBCO pancake coils are studied based on extended finite element method (XFEM). First, a two-dimensional axisymmetric finite element (FE) model is constructed and validated to study the stress distribution in an impregnated REBCO winding induced by thermal mismatch stress during cooling process from room temperature to 77 K. Furthermore, the delamination model is developed to character the delamination behavior of the impregnated superconducting windings based on XFEM, and the displacement-based failure criterion for the delamination of the impregnated REBCO winding is presented. Finally, the discussions of structure configuration effect on delamination is presented and evaluated through XFEM-based delamination model with displacement-based failure criterion. The results show that the presented model can well simulate the delamination induced by thermal mismatch during cooling process in impregnated REBCO coils. The displacement-based failure criterion according to XFEM-based delamination model can determine the failure critical temperature for winding's delamination. The discussions indicate that the influence of structure configuration on delamination performance of epoxy impregnated REBCO coils essentially depends on the radius ratio of outer to inner regardless of the coil size. A small radius ratio is suggested for the design of impregnated REBCO pancake coils.